This invention relates to electronic watch movements comprising analog time display means and more particularly those having only an hours hand and a minutes hand.
Such movements are generally intended to watches of small size, e.g. ladies' watches. In such watches, it is desirable for the cell to be as close as possible to the center of the watch. To this end, the movement described in swiss patent specification 615068 comprises a bottom-plate on which is provided a central peg on the dial side. On this peg are pivotally mounted the cannon-pinion and the hours wheel, which respectively mesh with the minutes wheel and the minutes pinion. The kinematic connection with the rotor is thus solely provided by the minutes gear. This arrangement enables the center of the movement to be cleared and hence a cell of large diameter to be used, but gives rise to a major drawback: since the cannon-pinion is at the end of the kinematic chain provided by the gear-train and thus, necessarily, has only few teeth, the backlash is quite substantial. As a result, the position of the minutes hand becomes somewhat inaccurate, unless a brake is applied on the cannon-pinion. But such a brake would increase the energy consumption of the watch and a larger cell would then be needed to achieve a corresponding autonomy.
In the specification of Japanese patent application 57-161578, a movement is described having a bottom-plate, a gear-train bridge, a rotor, an intermediate gear and an hours wheel. The center gear has a shaft that is pivotally mounted between the bridge and the bottom-plate and on which a wheel web is frictionally mounted. The shaft takes up the entire height of the movement while the wheel web is housed in a space between the bottom-plate and the cell. This arrangement lends itself to the design of a watch in which the cell extends close to the center without giving rise to a backlash problem with the center gear. But this result is achieved at the expense of the thickness of the cell.